Devices that provide navigation guidance to a driver in a vehicle are well known. In conventional systems, a navigation unit is installed in the vehicle. The navigation unit typically has an interactive visual screen or buttons that allow a driver to enter a desired destination location. The navigation unit has memory or a CD drive that keeps map data and a processor that generates a route based on the map data and desired destination. Conventional navigation units having map data and map generation processors are expensive. They also require a user to update the map data and do not permit the unit to select a route based on other considerations such as current traffic patterns or delays.
There has been increasing interest in server-based navigation systems. A server-based navigation system typically downloads information to a navigation unit or client device by wireless communications. The downloaded information contains the topology or other attribute information much like the original map information. The downloaded information can become quite large and may conflict with the memory size or connection limits of the client device. Different types of client devices (by different manufacturers) contain varying memory sizes. The wireless connection service used by a client device may also have varying coverage or bandwidth constraints. A portion of, or all of, the route information may be lost if the data file containing the route information is larger than the available memory size of the client device. Additionally, a part or all of the route information may be lost if the transmittal of the information occurs within an area having limited coverage or bandwidth.
Accordingly, there is a need to provide server-based navigation systems that can handle different types of client devices. Additionally, there is a need to handle situations where a calculated route passes through an area having limited coverage or bandwidth. It is, therefore, desirable to provide an improved server-based navigation system and method to overcome or minimize most, if not all, of the preceding problems.
While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.